Belts are known for use in motors such as automobile engines for power transmission. The belts can be toothed belts to reduce belt slippage and increase efficiency. The belts can be V-ribbed belts used to drive a plurality of auxiliary automotive apparatuses, e.g., an alternator, air conditioner and the like.
A conventional toothed belt includes a toothed portion and a back portion. The portions can be made of a rubber material that includes chloroprene rubber. A core, load bearing wire can be embedded in the back portion to increase belt strength. The core wire can be glass fiber cords bonded to the back portion with a resorcinol-formalin latex (RFL) solution containing styrene-butadiene rubber (SBR)-vinylpyridine latex as the latex component. A sheath of toothed cloth having shrink-wrapped nylon warps extending in the longitudinal direction of the belt can be placed over the teeth to extend the life of the belt.
A conventional V-ribbed belt includes a layer of bonding rubber and a layer of compressed rubber having at least two rib members extending in the longitudinal direction of the belt. The V-fibbed belt is stretched in a serpentine manner around a plurality of pulleys mounted to the auxiliary apparatuses to cause simultaneous rotation by communicating to the pulleys the rotation of a pulley mounted on an automotive crank shaft. This stretching requires that the V-ribbed belt have a high degree of bending and heat resistance.
The working temperature in an automotive engine compartment to which the toothed or V-ribbed belt is exposed has become higher due to the engine compartment being compacted and front wheel drive becoming more popular. The conventional toothed belt often falls at these higher temperatures because of chloroprene rubber failure which results in loss of teeth due to cracks developed on the back rubber potion and the dedendums or because of being cut due to bending-induced deterioration of the core wire. The conventional V-fibbed belt also experiences failure due to cracking of the rubber and bending deterioration of the core wire.
In response to the desire to extend the life of the belt, rubber materials using heat resistant elastomers such as hydrogenated chloroprene, hydrogenated aerylonitrilebutadiene rubber (HNBR) (obtained by hydrogenating acrylonitrile-butadiene copolymers) and chlorosulfonated polyethylene (CSM) have been used in the rubber material. Heat resistant rubber material is disclosed, for example, in Japanese patent laid open 62-159827.
The increasing severity of the working environment in automobiles, coupled with the requirement for a longer belt life, demand that rubber materials have a far better heat resistance than conventional rubber material. Among the three heat resistant elastomers disclosed above, the HNBR is more widely used because of its desirable heat resistance and oil resistance. The HNBR is used mostly in the form of a sulfur vulcanized rubber when the belt must also exhibit good dynamic characteristics, e.g., dynamic fatigue strength and dynamic deformation. Sulfur, either alone or in combination with vulcanizing accelerators such as thiuram, thiazole, sulfenamide compounds, sulfurylamide components and the like, is used in a system to vulcanize the HNBR.
With this vulcanization system, the quantity of sulfur is known to greatly influence not only the heat resistance but also influence the HNBR's dynamic characteristics. A decrease in the quantity of sulfur results in an increase in heat resistance and a diminishing of desirable dynamic characteristics. An increase in the quantity of sulfur results in a decrease in the heat resistance and an improvement in desirable dynamic characteristics.
Optimizing the iodine value (number) of HNBR and the quantity of the sulfur to be compounded with the HNBR suffers from a natural limitation to the improvement of heat resistance, although the limitation slightly varies depending on the combination with the aging retardant.
A rubber composition and belts made from that rubber composition that overcome at least one of the above-discussed shortcomings are desirable. The present rubber composition and belts satisfy this desire.